The invention relates to a surgical drilling apparatus for perforating the cranium including a drill plate which can be placed upon the cranium and a drill which is guided in the drill plate.
Drilling apparatus of this type are needed when it is necessary to install a ventricle drainage system so as to relieve the pressure in the interior of the skull for example. Hereby, it is known to use drill plates through which a drill provided with a handpiece is inserted (U.S. Pat. No. 4,821,716). With these, the operator presses the drill against the cranium and the drill is rotated until the skull has been penetrated. However, there is a danger here that avoidable injuries may be produced by maladroit application of pressure to the hand drill.
The object of the invention is to design a surgical drilling apparatus of the above type such that, when using it during the drilling process, injuries will be avoided in so far as possible.
In accordance with the invention, this object is achieved in the case of a surgical drilling apparatus of the type mentioned hereinabove, in that the drill is accommodated in a mounting which is rotatably mounted on the drill plate, said drill being displaceable along the rotational axis and being accommodated so as to be non-rotatable relative to said mounting, and in that the drill is displaceable towards the mounting against the effect of a spring.
Consequently, by virtue of such a design, the drill is pressed against the cranium with a defined spring force so that the axial force effective on the drill is independent of how strongly the user presses the drill plate and a drive means for the drill against the cranium. The pressure applied by the drill is determined by the spring alone, and consequently is selectable such as to ensure that cerebral tissue located below the cranium will be subjected to as little injury as possible.
It is expedient if a stop is provided for limiting the displacement of the drill relative to the mounting produced by the effect of the spring. It is thereby ensured that the drill is held captive in the mounting in an axial direction prior to the drill being placed on the cranium.
Furthermore, it is advantageous if the drill carries a stop for limiting the drilling depth, for example, in the form of a flange which can be placed on the upper surface of the cranium. This stop limits the depth to which the drill can penetrate into the cranium and can be selected such that the cranium will just be penetrated without the drill thereby entering substantially into the underlying cranial tissue and thus causing injuries thereto.
In a preferred embodiment, the mounting comprises a blind bore for accommodating the drill. The resultant construction is thereby very compact. It is expedient hereby if a spring, which pushes the drill out therefrom, is disposed in the blind bore i.e. the spring which presses the drill against the cranium with the desired spring force.
The drill may be driven in various manners, possibly by means of a motor, but in most cases the drive will be effected manually.
Thus, provision may be made for the mounting to be provided with a threaded guide means for a handpiece which engages the threaded guide means and is mounted thereon such as to be longitudinally displaceable therealong. Such a handpiece can be moved backwards and forwards along the threaded guide means thereby rotating the mounting and hence the drill.
In another embodiment, provision is made for the mounting to carry a gear wheel that engages directly or indirectly with a crown wheel which is rotatably mounted on the drill plate and is rotatable by means of a handle element.
It is expedient hereby if the crown wheel is disposed on the inner wall of a cap shaped handle element which surrounds the drill plate. Such a drill plate is thus of very compact construction and, moreover, it is also provided with an integral drive means for the drill.
The drill plate may, for example, be in the form of a cylinder and may comprise a plurality of support feet for resting it on the cranium whereby, in particular, three support feet may be provided.
In accordance with a preferred embodiment, provision is made for the drill plate to carry a marking element around its periphery for the purposes of positioning it on the cranium. This marking element enables the surgeon to place the drill plate on the cranium at a very specific position thereby ensuring that the drilling process will take place at the desired spot.
In particular, the marking element may comprise two right-angled delimiting lines. These delimiting lines can be aligned with corresponding marking lines which the surgeon has drawn on the cranium, for example, these marking lines could be connecting lines extending from ear to ear on the one hand and connecting lines extending at right angles thereto from the root of the nose to the centre of the back of the head. If the corner of the right-angled marking element is placed exactly at the crossing point of the two lines, and if the delimiting lines extend exactly in parallel with the connecting lines, then the precise position for the drill plate on the cranium is defined.
It would also be possible for the drill plate to comprise a lateral projection having side faces extending at right angles to one another, and for the side faces to flow tangentially into the outer contour of the drill plate. This could be effected over the whole height of the housing for the drill plate, but provision could be made for the projection to be provided only in the region of a flange on the drill plate on the side thereof facing the skull.